A NOVEL ELECTRICAL SERVO VARIABLE DISPLACEMENT HYDRAULIC PUMP USED FOR INTEGRATED ACTUATOR IN MEA

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1 28 TH INTERNATIONAL CONGRESS OF THE AERONAUTICAL SCIENCES A NOVEL ELECTRICAL SERVO VARIABLE DISPLACEMENT HYDRAULIC PUMP USED FOR INTEGRATED ACTUATOR IN MEA FU Yongling*,QI Haitao*, LU Yueliang**,GUO Rongsheng**,LI Zhufeng*,XUE Jing*, YANG Qi* * Beiing University of Aeronautics and Astronautics **AVIC Jincheng Naning Engineering Institute of Aircraft Systems fuyongling@26.com eywords: MEA, EHA, electrical servo, variale pump, PBW Astract The More Electric Aircrafts(MEAs) such as A38 and B787 apply the Electro-Hydrostatic Actuator (EHA)/ Electro-Mechanical Actuator (EMA)/ Electrical Back-up Hydrostatic Actuator (EBHA) to drive the flight control actuations surfaces.now the PBW actuators have een widely applied into more control surfaces. Such kinds of actuators have shown very good advantages. Next generation aircrafts will use more EHA and EMA. EHA requires the servo motor and servo pump for high performances. Among many kinds of EHAs, the EHA-Variale-displacement Pump(VP) is of its etter characteristics. In this paper, an electrical servo variale pump is developed for EHA, and the adapted electrical variale servo mechanism is designed. Simulation and analysis show that this kind of servo pump is of very good performances that suited for Power-By- Wire(PBW)actuators. In the end, the experiment results are given and compared with theoretical one. It is indicated that this electrical servo variale pump has a good prospect of application. General Introduction EHA is one development directions of the PBW actuators, one of the key su-technologies of MEA, and the main way of the new aircraft actuating systems. EHA is one of volume control methods that means varying the system flow y controlling the speed of the motor and the displacement of the pump in the integrated hydraulic system and thus controls the output of the actuator. Based on the differences in the electric motors, pumps and control methods, EHA can e divided into three types, which are fixed displacement variale speed(eha-fpvm), variale displacement fixed speed(eha-vpfm) and variale displacement variale speed (EHA- VPVM). By using dual-variale control, EHA- VPVM regulates the speed of the motor and the displacement of the pump at the same time, which increases a regulating freedom apiece compared to EHA-FPVM and EHA-VPFM that s why it comes true that the power of the motor exactly matches the system requirements, and improves the rigidity of the system and makes the performance of the system etter[~4].the method not only improves dynamic performance of the system ut also reduces the heat. Direct-axis axial plunger pump varies the output flow with regulating the angle of inclination of the swash plate y the pump variale institutions. The actuating part of the variale displacement mechanism in conventional servo pump is mostly driven y hydraulic servo system, which controls a hydraulic cylinder to drive the variale displacement mechanism and regulate the displacement of the pump. The working fluid of the variale displacement mechanism is provided y either the hydraulic system directly or a small pump coaxial with the variale pump. This way is technically more mature, and has a

2 FU YONGLING,QI HAITAO, LU YUELIANG,GUO RONGSHENG,LI ZHUFENG,XUE JING good response performance, however, the complex structure of the additional hydraulic actuator and the introduced sophisticated servo valve link increase the failure rate and losses of the system. The system pressure and motor speed of the EHA are not constant, so the driving force of the variale displacement mechanism must e provided another way. With the development of motor technology, the performance of servo motor has een greatly improved; the output power and response characteristics of servo motors can meet the demand in some low-power high-performance applications. In this paper, an electric variale servo pump was developed to resolve those contradictions aove, which drive the variale displacement mechanism of the servo pump y a DC servo motor through a gear transmission to provide a strong guarantee to EHA-VPVM. 2 Structure Design The electric servo variale displacement pump uses a high-precision gear which is driven y a DC servo motor to regulate the swing angle of the swash plate in the variale plunger pump and thus the displacement varies. The method actualizes a variale displacement servo drive without servo valves, the structure is shown in Figure [5~6]. servo motor and gear ox sector gear swash plate servo valve cylinder A)Contrast Between New And Traditional Design swash plate regulating motor and gear ox valve plate swash plate sector gear B)Schematic of New Design Fig.. Schematic of Electric Variale Servo Pump The actuating part of the variale displacement mechanism in conventional servo pump is a reciprocating hydraulic cylinder, which drive the swash plate to regulate the displacement with the moment arm. The servo valve and the cylinder are installed within the pump housing. The power density of the electric actuator is much smaller than the hydraulic actuator, therefore it is very difficult to place the variale mechanism within the pump housing. By using the rotary motor, the rotary motion of the motor can directly drive the swash plate with decelerating gear instead of converting into linear motion, therey we can avoid the prolems rought aout y the hinging of the two ends of the actuating mechanism while the perpendicular displacement of the swash plate changing with the actuating mechanism moving straightly. Therefore, the ody of the variale displacement pump is reconstructed y using the actuating mechanism to drive the swing shaft of the swash plate directly through a sector gear instead of the servo valve and cylinder, shown in Figure. The sector gear locates outside the pump housing, and is rigidly coaxial with the swash plate. With the highperformance drag-cup DC servo motor and the matched integrated gearox module, the deceleration of the motor is considerale, and the size of the variale mechanism is reduced. The structure is shown in Figure 2. 2

3 A NOVEL ELECTRIACL SERVO VARIABLE DISPLACEMENT HYDRAULIC PUMP USED FOR INTEGRATED ACTUATOR IN MEA swash plate regulating motor sector gear interface for rev regulating motor Fig.2. Three-dimensional Structure Diagram of The Electric Variale Servo Pump 3 Modeling and Simulation Analysis of The Variale Mechanism Considering the inertia load and damping load, the open-loop transfer function of the DC servo motor that drives the swash plate is [7] as elow according to the potential alance equation, the torque alance equation, EMF equation and the electromagnetic torque equation [9], suected to the load torque M Las a external interference of the system, armature voltage U as the input, the motor speed ω as the output ω Cm = () U CeCm + ( J s + B )( Las + Ra ) in which U is the control voltage (V), I is the armature current (A), Ra is the armature resistance (Ω), La is the armature inductance (H), E is the ack EMF of the armature winding (V), J is the equivalent rotating inertia to the motor shaft (kgm2), Ce is the ack EMF constant (Vrad - s - ), C is the electromagnetic m torque constant (Nm/A), B is the load damping coefficient, Tl = La / Ra is the electromagnetic time constant. The total reduction ratio of the gearox and the sector gear in the swing angle driving mechanism of the swash plate is, then the angle of the swash plate is ω γ = (2) s The load torque M L on the motor y the swash plate is M M L = (3) The theoretical displacement of the variale displacement pump q is q = Q γ (4) The output flow Qf () s is Q f = Qωγ / 2π (5) In which Q is the flow coefficient of the pump and ω is the shaft speed of the pump (rad/s). The motor is controlled y a doule closed loop with current feedack i and speed feedack ω, so the whole position loop feedack is γ. The model is estalished as shown in Figure 3. Suected to the torque of the swash plate as an external interference, the open-loop transfer function is q Cm Q G = = U CeCm + ( J s + B )( Las + Ra ) s (6) in which there is an integral, it is a type I system. 3

4 FU YONGLING,QI HAITAO, LU YUELIANG,GUO RONGSHENG,LI ZHUFENG,XUE JING γ ref U L i R α s + α i c M L C m M c 2 sign ( γ ) p ω γ + sign( ω ) J s + B a f ω s γ Q q f 2π c p f ω Q E C e ω γ ig.3. The Block Diagram of The Electric Variale Servo Pump System The mathematical model aove is simulated in MATLAB/Simulink. The maximum displacement of the variale pump is 2.5ml/r, the maximum speed is rpm, the swing angle range of the swash plate is±5, the power of the DC servo motor driving the swash plate is 85W, and the rated speed is 5rpm. By ignoring the nonlinear components in the system, the result of the linear analysis, the open-loop and closed loop Bode plots of the electric servo variale pump, are shown in Figure 4. The phase margin of the open-loop is 89.6º, and the crossover frequency ω c is.77hz, which is far less than the corner frequency point, thus the system has a larger staility margin. According to the simulation results we can increase the open-loop amplification to improve the cutoff frequency, therey improving the rapidity. magnitude/db phase/deg 5-5 I/O:Input Point to Output Point Frequency(rad/s):.4e4+4 Magnitude(dB): I/O:Input Point to Output Point Frequency(rad/s):.77-8 Magnitude(dB): Fig.4. the Open-Loop and Closed Loop Bode Plots of The Electric Servo Variale Pump Because of the nonlinear components such as the saturation voltage, the saturation current, the friction, the clearance and the dead zone, the linear analysis of the system is not enough. Then we use a PID controller to control the external ring swing angle with a PI controller in the inner loop, the step response at the maximum load without an overshoot is shown in Figure 5. The response of small-signal sinusoidal input is shown in Figure 6, the given amplitude is.75, the frequency is 5Hz, and the response of the swash plate is.72, which can meet the requirements of the frequency response in the EHA system. The simulations results show that the output displacement of the designed servo pump can e regulated rapidly without overshoot, the settling time and the frequency response of small-signal can meet the requirements. swash Plate angle/rad swash Plate angle/rad step responses of different swash plate angles response time/s Fig.5. Series of Step Responses.8.6 input signal output signal time/s Fig.6. 5% Small Signal Frequency 4 Experiments The developed variale electric servo axial F 4

5 A NOVEL ELECTRIACL SERVO VARIABLE DISPLACEMENT HYDRAULIC PUMP USED FOR INTEGRATED ACTUATOR IN MEA plunger pump and the hydraulic system test-ed are shown in Figure 7 and Figure 8 respectively. Fig.7 Photos of The Pump Fig.8. The Hydraulic System Test-Bed 4. Experiments of Swash Plate Swing Angle Regulating [6-8] The step response curve of the servo system is shown in Figure 9. In which Red curve is the given signal, and the green curve is the response. The response of given sinusoidal signal is shown in Figure. step responses sinusoidal signal response time/ms Fig.9 Step Responses of The Motor time/ms Fig.. Sinusoidal Signal Response of The Motor It can e seen that the response of different amplitude of the position step signals are asically the same. Take the response of -5 (-.3ml/r) for an example, the rise time is 2ms,the overshoot is 2.3%, and the transition time of 5% error and is 3ms; When steps from -5 (-.3ml/r) to 5 (.3ml/r), the rise time is ms, the overshoot is 8%, and the transition time of 5% error and is 28ms. The system has fast response and high steady state accuracy. For a sinusoidal signal input, when the frequency is increased to 5.Hz, the amplitude attenuation is.445db and the phaseshift is 29.8,which shows that the andwidth of the position servo system of the swash plate swing angle regulating motor is at least 5.Hz. As the swash plate swing angle regulating motor comes with the controller, and communicates with the EHA-VPVM via serial ports, the higher frequency response cannot e tested due to the limitations of communication speed. 4.2 Experiment of The Whole Pump The pump flow in conditions of different load pressures and speeds are shown in Figure and Figure 2. flow/lmin - 88 Pf=2.2MPa Pf=5.MPa 77 Pf=.MPa Pf=5.MPa 66 Pf=2.MPa Pf=2.2MPa 55 Pf=5.MPa Pf=.MPa Pf=5.MPa 44 Pf=2.MPa rev/rpm Fig.. Flow-Rev Under Series of Pressures 88 n=5rpm 77 n=rpm n=2rpm 66 n=3rpm n=4rpm 55 n=5rpm n=6rpm 44 n=5rpm 33 n=rpm n=2rpm 22 n=3rpm n=4rpm n=5rpm n=6rpm pressure/mpa Fig.2. Flow-Pressure in Series of Revs flow/lmin - (L/m in ) (L/m in ) 5

6 FU YONGLING,QI HAITAO, LU YUELIANG,GUO RONGSHENG,LI ZHUFENG,XUE JING The volumetric efficiency of the pump is 95%. It can e seen from the figures that the reduction of the volumetric efficiency is little while the pressure increases, therefore the performance of the pump is relatively stale. 5 Conclusions An electric servo variale pump, in which the swash plate is driven y a DC motor, is designed to meet the requirements of variale pumps in EHA. According to simulation analysis and experimental research, we found that the pump has the following advantages: () The system is simplified y using a motor to actuate the swash plate directly instead of the hydraulic actuator and the oil sources; (2) The link of servo valve that is vulnerale to pollution removed, make the reliaility and antifouling of the pump e improved, and the control of EHA-VPVM system without servo valves e achieved; (3) The swash plate is directly actuated y a motor, therefore the system is no longer dependent on the main motor which drives the pump. The output flow rate can e achieved idirectional variale and consequently effectively, which improves the response characteristics of the system; (4) A position servo control system is composed y comining the emedded control system, therefore the pressure, power and flow can e regulated without other additional hydraulic components; (5) With the development of motor technology, the characteristics of fast dynamic response and high frequency response can meet the requirements of various hydraulic systems. In this paper, the developed system fully meets the requirements [7] through the motor that is used to drive the swash plate. Theoretical and experimental results show that the variale electric servo pump can significantly improve the dynamic characteristics of the EHA, and provide a very useful asic component for the application and development of the EHA. Acknowledgements Thanks for the support of the National Natural Science Foundation of China (56759) and the Ministry of Science and Technology Foundation for International Cooperation (2DFA7254), and also, we are grateful to the 33 institute in AVIC and Center of Mechatronics and Hydraulics in Naning for the strong supports in components manufacturing. References [] John A. Variale displacement electro-hydrostatic actuator. National Aerospace and Electronics Conference, Dayton, Vol. 2, paper numer, pp , 99. [2] Mare J.C. Simplified model of pressure regulated variale displacement pumps for the sizing of complex hydraulic systems. Fifth International Conference on Fluid Power Transmission and Control, Hangzhou, pp 49-55,2. [3] Li J., Fu Y.L., Wang Z.L. Present development status and key technology research of airorne electrohydrostatic actuation system. Aeronautical Manufacturing Technology, No., pp 73-77, 25. [4] Qi H.T., Fu Y.L. Simulation of Electro-hydrostatic Actuator Based on AMESim. Machine Tool & Hydraulics, Vol. 35, No.3, pp 84-86, 27. [5] Gao B., Fu Y.L, Pei Z.C., Qi H.T. Servo pump s electrically driven variale displacement mechanism. Chinese Journal of Mechanical Engineering, Vol. 42, No. 3, pp 84-87, 26. [6] Zhang Y. Research on Control System of Dualvariale Integrated Electro-Hydrostatic Actuator.Beiing University of Aeronautics and Astronautics,Beiing, 2. [7] Gao B. Research on electrical variale servo pump, Beiing University of Aeronautics and Astronautics,Beiing, 25. [8] De L.G. Research on Variale Displacement Controller of Integrated Electro-Hydrostatic Actuator, Beiing University of Aeronautics and Astronautics,Beiing,28. Copyright Statement The authors confirm that they, and/or their company or organization, hold copyright on all of the original material included in this paper. The authors also confirm that they have otained permission, from the copyright holder of any third party material included in this paper, to pulish it as part of their paper. The authors confirm that they give permission, or have otained permission from the copyright holder of this paper, for the pulication and distriution of this paper as part of the ICAS22 proceedings or as individual off-prints from the proceedings. 6